Nakazawa et al. (U.S. Pat. No. 4,833,272), herein incorporated by reference, have proposed a process for preparing polycarboxylic acids by subjecting a Diels-Alder adduct of maleic anhydride and a diene to oxidation with hydrogen peroxide in the presence of a catalyst selected from tungstic acid, molybdic acid or heteropolyacids thereof.
Venturello et al. (U.S. Pat. No. 4,543,079) have proposed oxidative cleavage of olefins or vicinal dihydroxy compounds by treatment with hydrogen peroxide in a biphasic aqueous liquid/organic liquid, in the presence of a catalyst. Catalysts include tungsten quaternary ammonium, phosphonium, arsonium or stibonium compounds. A mechanism for the reaction is presented by Venturello et al., J. Org. Chem., vol. 51 (1986), pages 1599-1601.
Fremery et al., in U.S. Pat. No. 3,284,492, have proposed preparing carboxylic acids by ozonization of olefinic bonds in an emulsion containing hydrogen peroxide.
Kawamoto et al. (U.S. Pat. No. 4,331,608) have recited a liquid phase catalytic process for co-oxidizing unsaturated compounds, including unsaturated alicyclic compounds, in which oxygen and an aldehyde are present, along with a ruthenium catalyst.
Inoue et al. (U.S. Pat. No. 3,535,367) have recited a process for preparing 4-hydroxycyclohexanecarboxylic acids by treating a cyclohexenecarboxylic acid with sulfuric acid and hydrolyzing a resulting intermediate.
The oxidation of tetrahydrophthalic acid or anhydride to butanetetracarboxylic acid, with nitric acid, generally in the presence of a vanadium catalyst, has been investigated by:
Hopff et al., U.S. Pat. No. 2,203,628; Ladd, U.S. Pat. No. 3,915,997; Johnson, GB Patent 510,638; Franz et al., Chem. and Ind., (London), Feb. 25, 1961, pages 250-251; Franz et al., J. Org. Chem., vol. 30 (1965), pages 1488-1491.
It is an object of this invention to provide a two-step process for the preparation of butanetetracarboxylic acids, in which a tetrahydrophthalic acid is oxidized with aqueous hydrogen peroxide to a corresponding 4,5-dihydroxyhexahydrophthalic compound, which is further oxidized to a butanetetracarboxylic acid with hydrogen peroxide in the presence of a metal-containing catalyst. Advantages of the process include better control over an exothermic process, than heretofore, and production of a cleaner reaction product.